1. Field of the Invention
This invention relates to an improved lead-free carbon resistor and a method for producing such a resistor.
Carbon resistors are useful, for example, in spark plugs and igniters, to suppress electromagnetic radiation in the radio frequency range arising in connection with spark discharge; this radiation can interfere with the operation of television and radio communication equipment and other electronic apparatus.
2. Description of the Prior Art
Carbon resistors, for use as suppressors of electromagnetic radiation resulting from spark discharge, and which are composed, for example, of conductive carbon mixed with a silicone resin or organic resin binder and a filler such as a lead borosilicate glass, are well known. Similar resistors are also known where a lead borosilicate glass serves as a binder, rather than as a filler. Also, various methods for producing resistors of the indicated kinds have heretofore been known and used.
U.S. Pat. No. 3,742,423 discloses a carbon composition resistor and a method for producing the disclosed resistor. This patent describes a resistor having a body containing a conductor such as carbon black and/or graphite, a silicone resin binder, and a non-conductive filler selected from the group consisting of silica, mica, wollastonite, asbestos, glass and mixtures thereof. The method of this reference as disclosed involves mixing and pulverizing the above-described components at a temperature below that at which cure of the silicone resin takes place. The mixture is then formed in a die into a shaped body while a similar low temperature is maintained. The shaped body, after removal from the die, is heated to a temperature of from 400 to 750 degrees F., for from 20 minutes to 2 hours, to cure the silicone resin.